Patent GB-684599-A (GB)
Title: Improvements in or relating to composite photographic film unit and process of treating same
IPC: G03C8/34
Filed: 1948-03-04
Abstract: 684,599. Self-processing photographic film units. STEVENS, A. H. (International) Polaroid Corporation). March 4, 1948, No. 6765/48. Class 98 (ii). The unit comprises a first layer including a photo-sensitive portion, a second layer superposed thereon and a plurality of rupturable containers placed to release their contained liquid to effect reactions within the unit. The first layer, 12, Fig. 1, may be of barytacoated paper or cellulose acetate dyed or backed with paper to make it light-impervious; the photo-sensitive portion 10 may comprise diazo compounds or ferric salts or, preferably, a silver halide emulsion; the second layer 14 may be of gelatin, sodium alginate or cellulose ethers or derivatives of such and is provided with a backing layer 16 preferably of a transparent cellulose ester; of the two rupturable containers shown 18 preferably contains a liquid composition to carry out formation of a visible image such as a negative image in the photo-sensitive portion 12, and, preferably by transfer of image-forming components, a positive image in the second layer 14; such liquid composition preferably comprising an aqueous solution of a developer such as hydroquinone, a film-forming substance such as sodium carboxymethyl cellulose, and sodium thiosulphate. Rupturable container 20 may contain a liquid film-forming substance such as the aforementioned sodium carboxymethyl cellulose and a pigment such as titanium dioxide, magnesium oxide or magnesium carbonate which will form an opaque white film; or may contain sodium carbonate which may react with another material provided in the unit to form a white substance such as colloidal zinc hydroxide; or may contain a dye, dye coupler or dye base. The containers 18, 20 are of the type disclosed in Specification 684,592 and in the case of roll film pairs of them are positioned at intervals along the length of the film. In use the unit of Fig. 1 is exposed as in a camera in the direction of the arrow, run through pressure means such as a wringer to break the containers and cause development of the latent image in portion 10, production of an equivalent positive as in the second layer 14, and an opaque background therefor, after which the first layer 14 with portion 10 are preferably stripped off, to reveal the positive image. Fig. 2 shows a modification of the unit which may be exposed in the reverse direction, and which includes a layer 26, as of hardened gelatin, of controlled permeability, whereby access of the liquid in container 20 to the photo-sensitized portion 10a may be delayed, and such liquid may include an acid such as maleic, citric or hydrochloric acid to neutralize the developer after the latter has performed its functions. Fig. 3 shows a modification with a third container 22, having therein a black dye to form a light barrier in the further layer 24 so that after exposure and release of the liquids from all the containers the unit may be ejected from a camera directly into daylight. Figs. 4 and 5 illustrate further modifications of the unit.